The present invention relates to a process for making a wet-layed metal fiber nonwoven sheet which also contains metal powder. In particular, the present invention relates to a process for making a metal fiber/metal powder sheet.
Papers comprised primarily of metal fibers have been desired by the industry for many years. Various methods have been developed for the preparation of metal fiber sheets. The manufacture of metal fiber nonwoven fabric-like paper structures on papermaking equipment has also been actively pursued due to its commercial attractiveness. Interest in such techniques is described, for example, in the chapter on metal fibers by Hanns F. Arledter in Synthetic Fibers in Papermaking, Editor O. Balestra, chapter 6, pages 118-184.
The problem in making metal fiber sheets using conventional papermaking techniques is that the metal fibers tend to clump together. Before paper can be made, it is necessary to open fiber bundles to achieve individual fibers and to disperse the fibers uniformly in a fluid. With most wood pulps, the opening is not usually a difficult task. The pulp or source of fibers is placed in water and the mixture is sheared until the bundles open.
With metal fibers, however, both the opening of the bundles and the dispersion of the fibers in order to keep the fibers separated are difficult. Normal types of mixing or shearing devices can easily damage metal fibers. When metal fibers are bent, they will remain bent and eventually will interact to form balls of tangled fibers. Paper made from fibers in this form is unacceptable.
It would be of great advantage to the industry, therefore, if a process for making a metal fiber sheet using conventional papermaking techniques, i.e., a wet-laying technique, can be used. Such a process should offer efficiency and commercial viability in terms of cost.
Moreover, the cost of a metal fiber sheet can be prohibitive. A metal sheet which is made of metal fiber but is more cost effective would also be attractive. A sheet containing metal fiber and metal powder would be such a sheet.
Accordingly, it is an object of the present invention to provide a metal fiber sheet which also contains a metal powder.
Yet another object of the present invention is to provide a process for making such a metal fiber/metal powder sheet using a wet laying technique.
These and other objects of the present invention will become apparent upon a review of the following specification, the figure of the drawing, and the claims appended hereto.
In accordance with the foregoing objectives, provided by the present invention is a wet-layed, nonwoven sheet which is comprised of metal fiber and metal powder. Generally, the amount of metal fiber comprises from 20 to 95% by weight and the amount of metal powder comprises from 5 to 80% by weight of the sheet. Such a wet-layed nonwoven sheet is economically preferable to a sheet comprised totally of metal fiber, since the metal powder is much less expensive. Among other factors, the present invention is based upon the recognition, using various process techniques, that the combination of metal fiber and metal powder can be wet-layed to obtain a structure of sufficient strength for subsequent handling and sintering.
In a preferred embodiment, the wet-layed nonwoven sheet comprised of metal fiber and metal powder is made by a process which involves first dispersing metal fibers and the metal powder into an aqueous dispensing fluid which contains a non-carboxy containing water soluble polymer. The aqueous dispensing fluid is then applied onto a screen, with the aqueous dispensing fluid then being removed to thereby form the metal fiber/metal powder sheet.
In another preferred embodiment, the wet-layed, nonwoven metal fiber/metal powder sheet of the present invention is made by a process which comprises first dispersing a mixture of the metal fiber, metal powder, wood pulp and a fibrillated material into an aqueous dispensing fluid. Generally, the amount of metal fiber and metal powder together ranges from 60 to 80 weight percent based upon the solids, the amount of wood pulp ranges from about 15 to about 30 weight percent, and the amount of fibrillated material ranges from about 5 to 15 weight percent based upon the weight of solids. The aqueous dispensing fluid is then applied onto a screen, and the fluid is removed to provide a metal fiber/metal powder sheet.